If you believe that your children were in danger at that campground and that he is a sexual deviant that intentionally let his children see his dick pics you are 110% right in getting them and doing whatever you can to keep them away from him.
If you believe that it was unintentional and he would password his phone after bringing it to his attention than it might be good to reflect on your motivation because if this is the case it was simply a maneuver to win another battle in your war with him and the kids were in the middle.
I don't know him and I don't know what kind of pictures they were so I've no idea which one - just throwing it out there because I don't think a dick pic makes anyone a pervert or a danger or should cause any child mental scarring but there is likely more to the story with his history etc.